It's not uncommon these days to hear talk of "lessons" learned in Vietnam and their application to current U.S. conflicts. Unfortunately, most observers have ignored the uniqueness of the Vietnam War, picking and choosing the lessons learned there with little regard for their application to the present.

This is particularly true with the current buzz over the "clear and hold" concept, which has gained popularity in some circles. Secretary of State Condoleezza Rice invoked it during Senate testimony in October, and columnist David Ignatius reported in his Nov. 4 op-ed that many Army officers are reading historian Lewis Sorley's book "A Better War," which argues that the United States could have prevailed in Vietnam if the military had used Gen. Creighton Abrams's ideas earlier in the war.

This simplistic notion may resonate in Washington, but it means little to troops on the ground. Marines in Fallujah or soldiers in Baghdad or near the Syrian border will tell you that they have been "clearing" areas for more than a year now, but "holding" them is a different matter. That takes a lot of troops, not small teams.

So much for simple lessons from Vietnam. But for better or worse, Vietnam is the most recent example of American counterinsurgency -- and our longest -- so it would be a mistake to reject it because of its complex and controversial nature. Stripped to essentials, there are three basic lessons from the war. All must be employed by any counterinsurgency effort, no matter what shape it takes.

First, there must be a unified structure that combines military and civilian pacification efforts. In Vietnam that organization was called CORDS, for Civil Operations and Rural Development Support. Formed in 1967, it placed the disjointed and ineffective civilian pacification programs under the military. This was accomplished only at the insistence of President Lyndon Johnson, who took an active interest in seeing the pacification process function smoothly under a single manager: Gen. William Westmoreland. CORDS gave the pacification effort access to military money and personnel, allowing programs to expand dramatically. In 1966 there were about 1,000 advisers involved in pacification, and the annual budget was $582 million; by 1969 that had risen to 7,600 advisers and almost $1.5 billion. This rapid progress was possible only because of CORDS's streamlined system under Defense Department control.

In Afghanistan, the provincial reconstruction teams have viewed CORDS as a model, but there is no truly integrated system yet. In Iraq, the old Coalition Provisional Authority suffered from the same problems that caused the formation of CORDS, in particular a dual chain of command that failed to coordinate military and civilian efforts. Not enough has been done since the CPA's dissolution in 2004 to integrate nation-building into military planning.

The second lesson involves attacking the enemy's center of gravity. An insurgency thrives only if it can maintain a permanent presence among the population, which in Vietnam was called the Viet Cong infrastructure, or VCI. This covert presence used carrot and stick -- promises of reform and threats of violence -- to take control of large chunks of the countryside. U.S. planners were aware of VCI, but until 1968 only the CIA paid it much attention. Under CORDS, however, the United States implemented the much-maligned Phoenix program, which targeted VCI and resulted in the capture or killing (mostly capture) of more than 80,000 VCI guerrillas. Criticisms of Phoenix abound, and there were many problems with the system, but the fact is that a counterinsurgency plan that ignores the guerrilla infrastructure is no plan at all.

The application of intelligence aimed at guerrillas' ability to live among the population is obvious. In Afghanistan, the Taliban are weak enough that their ability to influence the people is limited, but failure to watch them as they try to worm their way back into the villages will bring disaster later.

In Iraq, the situation is different in that the guerrillas have not made a concerted effort to mobilize the people. A large part of the Sunni population seems to support the insurgency, but the guerrillas are not forming local shadow governments or attempting to establish their own political and economic programs. Still, it makes sense to aim intelligence directly at the guerrillas' recruiting process to try to disrupt it.

Finally, it is crucial to form militias in order to raise the staff necessary to maintain a permanent government presence in dangerous areas. This is the only way "clear and hold" has any hope of working. Even an eventual U.S. troop strength of more than 500,000 and a similar number of South Vietnamese soldiers were not enough to take the countryside from the insurgents. But the early creation of a territorial militia helped return a government presence to the countryside. These militia members were recruited in villages and paid by the government; they lived in the areas where they operated, making it more difficult for the Viet Cong to settle among the population. Their numbers also reached 500,000, thanks partly to early participation by U.S. advisers. Although the militia's performance was sometimes lacking, overall it was an important part of the pacification program.

In Afghanistan and Iraq the lack of government-controlled militias is a serious weakness, and the United States has not pushed for their formation. Militias exist in both countries, but they are often loyal to warlords (Afghanistan) or under the command of various ethnic or religious groups (Iraq). Their allegiance to the government is questionable.

In the end America failed in Vietnam, and it is difficult to convince the public or policymakers that there is anything to learn from a losing effort. But the U.S. military did make important headway in pacification, and it would be foolish to let that experience slip away. Saigon's ultimate collapse was due to factors beyond the scope of counterinsurgency -- North Vietnam's large army and Washington's decision to allow it sanctuaries outside South Vietnam's borders were pivotal -- but the communist insurgency was badly hurt by pacification. In Afghanistan and Iraq none of these three lessons is being applied with any rigor, though there appears to be progress on the first two. But as one counterinsurgency expert told me, failure to employ all these basic tenets "doesn't mean you will lose the war, but you sure can't win."

The writer is a historian and author of "Ashes to Ashes: The Phoenix Program and the Vietnam War."